In this paper, I propose a Construction Grammar approach to the count/mass distinction in French. Rather than confine my analysis to NPs, I examine the effects of massive conversion in the broader context of two partially-filled idiomatic constructions: the CCDN construction (ça c'est de la voiture ! 'that's some car') and the CDN construction (cette voiture, c'est de la bombe ! 'that car rocks!'). Both inherit properties from the Copular Subject Predicate construction (c'est une voiture 'that's a car"), except their nominal predicates undergo count-to-mass conversion. Generally, count-to-mass conversion has a quantitative function: it turns NPs whose referents are numerically quantifiable into an NP whose referents cannot be quantified as separate entities. In the CCDN and the CDN, count- to-mass conversion has a qualitative function: it predicates a quality of the subject by identifying this subject with the prototype of the category denoted by the nominal predicate. I show that the CCDN and the CDN belong to the same constructional network, even if they differ as to the kinds of identification that they realize.